[palmtreepathos]

My only worry is that it might interfere with or cancel the draw of air. Like two fans blowing at each other. The air intake is 10cm stovepipe, so it would be like a low pressure fan, but the retort pipe would be much smaller, but probably at a much higher pressure.

the hot air that would be escaping the retort would actually be very flammable wood gas... a secondary souce of further flame. This is often done in charcoal makers. The pipe and pressure would also keep the flame from traveling back up into the retort. It may need to be capped when your burn is finished to restrict air intake as the char cools though.

[Fukudairafarm]

Ok, I decided to give it another try without re-routing the woodgas last weekend. I packed the 20L retort with split bamboo. This time I sealed the lid, and drilled a 5mm hole in the top. I tried to fit on a 90 degree elbow on the front of the stove, but it was not very effective. Lots of smoke and backdrafts. I finally was forced to remove the elbow and feed the stove horizontally as before.
Firing the stove with split bamboo, it took a LONG time before I saw any sort of outgassing. After an hour and a half of constant firing, some feeble wisps of steam began to come out. I kept on feeding it for another hour, but the ammount of steam/gas didn't get much bigger.
I have come to the conclusion that in the current configuration, it is not economical timewise to make charcoal in the retort.
I am still trying to figure out how to attach a pipe to the retort to direct the woodgas to the combustion chamber. Any ideas?

Some more observations-
-A sleeve around the retort should help it heat more quickly.
-Or perhaps just putting the rocket stove aside for a while, I have been toying with the idea of just putting the retort on a campfire and seeing what happens.
-Raising the interior chimney of the rocket stove (putting another can on the original stove with a taller chimney) could increase the draft enough to allow vertical feeding. But it would make the already none to stable configuration more unsteady.
-I just got the book Super-efficient woodstoves you can build by Ianto Evans a few days ago, and it really has some great ideas.

[Philip Small]

Originally Posted by Fukudairafarm

... I packed the 20L retort with split bamboo. ...

I am thinking that 20L is too large a retort in proportion to the 10cm stove.

... I am still trying to figure out how to attach a pipe to the retort to direct the woodgas to the combustion chamber. Any ideas? ...

Bulkhead connector. Any double-nut-able union, coupler or flare fitting might be adaptable, maybe even a simple threaded nipple, if long enough. Brass fittings at automotive/plumbing supply store?

... I have been toying with the idea of just putting the retort on a campfire ...

I recommend as a good learning experience. Also, retort is the best way to make writing charcoal, char cloth for flint-and-steel fire starting, and where char uniformity and consistency is of value.

...Raising the interior chimney of the rocket stove ... But it would make the already none to stable configuration more unsteady. ...

More draft is a brilliant option, may address retort oversize concern I have as well as your feed hopper challenge. If you layer the base of your rocket with sand/gravel instead of ash, bet the stability increases.

... Super-efficient woodstoves you can build by Ianto Evans a few days ago, and it really has some great ideas ....

Lucky.

Phil

[Fukudairafarm]

well, I am fed up with Japanese hardware stores. I have been searching for any sort of metallic hose fittings/nozzles, couplings, fittings or nipples, or bendable metallic tubing, but have found only plastic. When I asked the clerk at the local home center, he looked at me like I was some sort of dinosaur. I may have to ask my dad to send me a package of copper tubing. He will probably think I am building a still... Hey, not a bad idea tho...

Oh, and Phil, I also wondered about lining the base of the stove with sand, but the Evan's book says that might not work as well because of the high thermal mass. A low mass insulated interior chimney is preferrable apparently. But I think I would trade some initial efficiency for some stability... If I ever get some metal fittings to run a pipe, do you think I should attach it to the top, bottom or middle of the retort?

[Philip Small]

Originally Posted by Fukudairafarm

I also wondered about lining the base of the stove with sand, but the Evan's book says that might not work as well because of the high thermal mass. A low mass insulated interior chimney is preferrable apparently. But I think I would trade some initial efficiency for some stability... If I ever get some metal fittings to run a pipe, do you think I should attach it to the top, bottom or middle of the retort?

No doubt mass around the elbow changes how responsive the draft is to changes in heat intensity. On a small stove, like yours, that could be pretty important.

A Justa (see here and here) named for Doña Justa Nuñez of Suyapa, Honduras who helped to design it, is a rocket-based stove adapted to indoor cooking that uses masonry. The first link mentions "with ceramic bricks used for the combustion chamber". High thermal mass in the elbow area may not be ideal but it is not unworkable.

Ideally in your config, the elbow would be high enough that you would have room to separate a bottom layer of sand from the elbow with ash or vermicullite. Even 20-50 mm separation would help keep the draft bright. Another thought is a ring of cement inside the bottom, well separated from the elbow. Wouldn't be hard to make a form for this.

I would attach the gas relief tube to the underbelly of the retort. If the tube is small enough to bend without pinching it, I would run it down along (close or touching) the inside of the flue and, at the discharge end, give it a turn to direct the woodgas up the flue.

Hope this all works in reality as well as it does in my imagination.

Flame on!

[Philip Small]

Originally Posted by Philip Small

High thermal mass in the elbow area may not be ideal but it is not unworkable.

Update: I have since learned, from pdfs here and here, that the body of the Doña Justa stove is partly filled with earth and insulated with ash. Makes sense.

[Fukudairafarm]

Update:
Well, I finally got around to working on a new rocket stove for the project. The new stove is a brick tower vertical feeder. I just cobbled it together this morning and took it for a test run before I mortar it in place. Even just dry fit, with quite a few gaps, it worked great!

If you have some spare brick laying around, it is easy to put together.
(Pictures hopefully coming soon, until then)
The lowest level is 8 bricks on edge in a long rectangle. (three each side, one each end)
The second level is the same (of course staggered).
On the third level, I made two squares, one on each end of the rectangle, and filled in the middle with three bricks on edge
Then I just built a chimney on one end to six bricks high.
That ended the construction.

To light it was a breeze too. I just crumpled up some newspaper and put it in the bottom of the feedbox and lit it.
When it was going, I took some very fine split wood (a little thicker than disposable chopsticks) and stood it up in the feeding hopper upstream of the paper. The fire backed into it, and started roaring down the tunnel and up the chimney. (I did have to blow once or twice down the feedbox to make the fire start down the tunnel and begin to draw)
After that, I just stood up some split bamboo in the feed hopper behind the wood, and it ate into that too. The material in the front burns from the tip, and gravity feeds it down.
On trick is to lever the older material towards the front when you add the newer in the back.

After I get it mortared together, I plan to insulate the thing with some vermiculite, maybe with a light clay slip so it will stick together (think "hypertufa" with clay instead of cement). I think that will really improve the efficiency as well.

Coming soon: Making a skirt for the retort to keep the wind from robbing all my heat.
Also, I finally got some 1/2 inch outside diameter copper tubing (thanks Dad!) and will be working on the woodgas feed over the weekend (I hope). The latest idea is to drill a 1/2" hole in the lid, loose fit the tube and arrange it to the firebox, and finally seal the junction with either a stiff flour dough or some sand/clay. It would break everytime you moved it, but it wouldn't cost anything.

[Fukudairafarm]

Wow, sorry it has taken so long to get back to this- I have been swamped with everything else.
Well, I finally got around to mortaring the brick rocket up. Well, it isn't really mortar, more along the lines of sand-clay (70-30)

Pictures-






I split some dry old pine and fired it up. Worked quite well, no visible leaks.

I was thinking of filling the retort with pine cones, cedar branches, or rice straw. Or even the chestnut burrs that make sitting down around here such a risky proposition... Or maybe a nice mix of all of them.
Any other suggestions for things to try and char?

Happy Gardening!

[Turtle]

Originally Posted by Fukudairafarm

Wow, sorry it has taken so long to get back to this- I have been swamped with everything else.
Well, I finally got around to mortaring the brick rocket up. Well, it isn't really mortar, more along the lines of sand-clay (70-30)

Pictures-
Attachment 1909

Attachment 1910

Attachment 1911

I split some dry old pine and fired it up. Worked quite well, no visible leaks.

I was thinking of filling the retort with pine cones, cedar branches, or rice straw. Or even the chestnut burrs that make sitting down around here such a risky proposition... Or maybe a nice mix of all of them.
Any other suggestions for things to try and char?

Happy Gardening!

Nice work! You inspired me to try the rocket stove from coffee-cans idea I have been toying with. I spent about 45 minutes putting it together. It works pretty well, but can use some improvements.

I wasn't really going for charcoal, rather a portable camp stove, but I got about 3/4 cup anyway.

I think I'll add a blow tube as it needs help getting air when starting and after adding fuel; gets pretty smoky. Also probably need a few more intake holes on the top plate. Runs like a dream when all fired up though.

YouTube - Coffee can rocket stove

[Fukudairafarm]

Wow Turtle, looks great! I would like to try building one of those as well.
I wonder how long it would take to boil a litre of water.... I sense an experiment in the works...